The invention relates to a monitoring OAM cell assisted method enabling continuous intrasystem determination of bit errors which have occurred in ATM useful cells with a useful information field and a cell head on an ATM transmission link. This method comprises the generation of control bits by evaluating bits of ATM useful cells with a selected target address in the cell head prior to feeding the ATM useful cells into the ATM transmission link, whereupon said control bits are additionally encoded thus generating further control bits. As a next step, in addition to the ATM useful cells, the monitoring OAM cells are transmitted on the ATM transmission link together with the one control bits and the further control bits. The further control bits of the monitoring OAM cells received at the other end of the ATM transmission link are then examined as to whether the respective monitoring OAM cells were transmitted without error and the bit errors which have occurred in the related received ATM useful cells are determined by means of the one control bits of the monitoring OAM cells recognized as having been transmitted error-free.
In a known method of this kind (Andreas Wolf, `Leistungsmessungen in ATM-Netzen`, NTZ volume 47, issue 6, 1994, pages 408 to 413) monitoring OAM cells are used for continuous intrasystem monitoring of an ATM transmission link. For this purpose, the monitoring OAM cells are introduced into the cell stream of the ATM useful cells. EDC data (EDC: error detecting code) contained in the useful data of said monitoring OAM cells allows the detection of bit errors in ATM useful cells. In practice, only ATM useful cells with a selected target address in the cell head are used. According to the above-quoted prior art, the useful data of the monitoring OAM cells furthermore include ECB data (ECB: error check bits) allowing the detection of bit errors in the monitoring OAM cell in question. To be more precise, this is the cyclic supplementation of an Abramson code which makes it possible to detect up to three bit errors. If, during a verification of the ECB data, errors are detected in one of the monitoring OAM cells, such cell is eliminated and not used for evaluation.